1. Field of the Invention
The present invention relates to a defect inspection apparatus and a defect inspection method for inspecting a defect in a semiconductor wafer or a liquid crystal substrate.
2. Description of the Related Art
In a manufacturing process of semiconductor circuit elements and liquid crystal display elements, a defect inspection is performed for repetitive patterns formed in a resist layer on a surface of a semiconductor wafer or a liquid crystal substrate (generally referred to as a substrate). An automated defect inspection apparatus has a substrate placed on a tiltable stage, irradiates the surface of the substrate with illumination light for inspection, captures an image of the substrate according to the light (for example, primary diffracted light or specular light) that emerges from the repetitive patterns on the substrate, and detects a defect in the repetitive pattern based on brightness information on the image (for example, refer to Japanese Unexamined Patent Application Publication No. 2002-162367). Further, by adjusting the tilt of the stage, it is possible to perform the defect inspection for repetitive patterns having different pitches. Also, it is possible to cope with minute pitches by shortening the wavelength of illumination light.
However, the brightness information of the image captured for defect inspection contains not only defect information of the repetitive patterns formed in the resist layer as the uppermost layer but also information resulting from noise light from the underlying layer. Therefore, in the prior art there are some cases where a large amount of the noise light from the underlying layer prevents a defect inspection with a good S/N ratio (for example, where repetitive patterns are formed in the underlying layer with a pitch which is approximately the same as that of a resist layer, etc.). Note that the noise light from the underlying layer is part of illumination light for inspection that has once passed through the resist layer, reached and reflected from (diffracted by) the underlying layer, and passed through the resist layer again.